Most of industrially produced polymeric materials, oils and lubricants need the presence of intentionally added substances to ensure required stability during their processing, storing and using in finished articles. These substances retard or inhibit undesirable oxidation phenomena in a given substrate, so that they prevent complete deterioration by the influence of oxygen, increased temperature, UV radiation and mechanical stress.
The above requirements are met by substances showing anti-oxidative effect. To the best-known and most often used of these, there belongs the group of aminic anti-degradants, for example N-phenyl-1-naphthylamine, N-(4-tert-octylphenyl)-naphthylamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine (CS AO 261 085 and CS AO 226 248). They can be easily modified and it is possible to obtain substances having properties required for a broad spectrum of various materials; as well as processing and exploitative conditions of use.
Alkylated diphenylamines are effective in oils, lubricants for turbine machines, aircrafts and everywhere, where there is high working temperature, and in combination with other additives they ensure high anti-oxidative and thermal protection (CS AO 226 248, U.S. Pat. No. 3,414,618). They are usually slightly colouring, resistant against further turning yellow in comparison with unsubstituted diphenylamine, which besides the anti-oxidative properties tends to turn yellow in rubber mixtures.
Alkylated diphenylamines are most often prepared by typical Friedel-Crafts reaction of alkylation of aromatic amines by olefins. Industrial alkylations utilise the typical Friedel-Crafts catalyst AlCl3. Also other catalysts, like for example H2SO4, anhydrous HF, H3PO4 on carriers, various aluminosilicates, zeolites, pillared clays, are suitable. Advantages of AlCl3 are its high catalytic activity and insolubility in organic substances, disadvantages are its high sensitivity to the presence of water, corrosive properties, demanding way of removing it from the reaction mixture, as well as that a great amount of waste-waters arises, presence of chlorine in the products and presence of undesirable, by-products, including those which are alkylated at nitrogen.
AlCl3 belongs to efficient alkylation catalysts for diphenylamine which, besides the fact that it accelerates alkylation to positions 4, 4′ of diphenylamine, catalyses also cleaving reactions provided the reactant is diisobutylene. There arise tert-butyl derivatives and in the subsequent reactions considerable amounts of trioctyldiphenylamine, thus causing decrease in the amount of the desirable 4,4′-dioctyldiphenylamine. This weak points are partially solved by using catalysts based on bentonite (U.S. Pat. No. 6,315,925). Use of some aluminosilicates without preceding activation is described in SU 443 026. Disadvantages of this process are low activity of the catalyst and its variable quality, even if from one source. Natural aluminosilicates are also activated by an acid to increase their catalytic efficiency (U.S. Pat. Nos. 2,943,112, 4,163,757, 4,824,601). The disadvantages of using catalysts based on bentonite according to the above U.S. patents are low concentration of 4,4′-dioctyldiphenylamine and high content of unreacted diphenylamine—up to 5%.
Alkylation of aromatic amines is performed by alkylating agents which are prevailingly constituted by olefins, especially isobutene, diisobutylene, nonene, styrene, alphamethylstyrene (U.S. Pat. Nos. 2,943,112, 3,714,258, published SK PP 743-98); the alkene may further be pentene-1, hexene-1, heptene-1, octane-1, nonene-1 or their mixtures. Alkylation of aromatic amines by, for example, nonene is described in SK PP 743-98, where four- to tenfold mole excess of nonene, referred to diphenylamine, is used for preparation of the resulting product, and the alkylation is performed at a temperature of 150 to-220° C. The disadvantages of this method are the relatively high temperature and high excess of nonene which must be subsequently removed from the reaction mixture for the purpose of regeneration, thus together with the high reaction temperature increasing the production costs.
In U.S. Pat. No. 5,672,752, there is described the use of a catalyst based on bentonite which is preferred in the process of monoalkylation over dialkylation at specific conditions, like temperature and mole ratio of diphenylamine to diisobutylene (DFA: DIB). A disadvantage of this method is the fact that it does not provide a product having the required amount of 4,4′-dioctyidiphenylamine. Alkylation of DFA by diisobutylene using activated aluminosilicate, is described in U.S. Pat. No. 5,520,848. Synthesis of 4,4′-dioctyldiphenylamine from DFA and DIB with its content less than 25% in the reaction mixture using activated clay, like the catalyst Fulcat 22B, is described in U.S. Pat. No. 4,824,601. Nevertheless, the reaction product still contains 10% of unreacted DFA.
Moreover, a disadvantage of all above processes is, as already mentioned, relatively low concentration of 4,4′-dioctyldiphenylamine—less than 30%.
The aim of the present invention is to present a method of preparation of antioxidant composition on the basis of diphenylamine.